Conventionally, there has been known a gas sensor which detects the concentration of a specific gas component of an object gas, such as exhaust gas discharged from, for example, an automobile. Such a gas sensor uses a gas sensor element whose electrical characteristic changes in accordance with the concentration of the specific gas component of the object gas. A known gas sensor element is configured such that a pair of electrodes are formed on a solid electrolyte member mainly formed of zirconia, and an insulating layer, a heater, etc. are laminated thereon, whereby the gas sensor element assumes a plate-like outer shape as a whole.
In the above-described gas sensor element, the insulating layer is formed of ceramic whose predominant component is alumina, which is excellent in insulating property and heat resistance. The heater has a structure in which a heating resistor or the like is buried in a heater insulating layer formed of a ceramic material whose predominant component is alumina (for example, see Patent Document 1).